1. Technical Field
Present invention relates to a process for fabricating a superconducting joint, particularly to a process for fabricating a superconducting joint for high magnetic field superconducting magnets.
2. Background Art
Low-resistance superconducting joints are key techniques to develop high stability, high magnetic field superconducting magnet systems. Such magnet systems are mainly used in scientific instruments, medical diagnosis, special electric equipments and so on. Generally, due to special application requirements of high magnetic field scientific instruments, the resistance of joints for superconducting wires should be less than 10−13 ohm to 10−14 ohm. The low resistance of joints for superconducting wires is important to achieving a highly stable magnetic field in superconducting scientific instruments. Therefore, it is desirable to develop a process for fabricating special joints to achieve stable magnetic field characteristics, and to carry out testing of material structures and realize special functions. At present, the superconducting magnets prepared with superconducting materials such as niobium-titanium (NbTi) and niobium-tin (Nb3Sn) and the like can generate relatively high magnetic fields. Generally, if the magnetic field provided by superconducting magnets is 10 T or less, NbTi superconducting wires can be used to develop superconducting magnets to meet this requirement. If the magnetic field of superconducting magnets is 10 T or more, a combination of NbTi and Nb3Sn needs to be used. To achieve magnets operated in persistent mode, it is necessary to connect superconducting magnets using joints with ultra low resistance via superconducting switches, to form a magnetic field with a very low rate of field decay.
At present, the processes for fabricating joints of high magnetic field superconducting magnets mainly include cold welding, ultrasonic welding, laser welding and resistance brazing, etc. Since the resistance of a superconducting joint depends on different processes and conditions, and meanwhile magnets are large in size, the processes for fabricating the joints should be as simple and reliable as possible. When the background magnetic field is relatively high, the critical transmission current decreases greatly. In order to obtain superconducting joints having high transmission current and low contact resistance under high magnetic field, it is desirable to develop a process for fabricating more advanced magnet joints.